Her fiance, Ian Stewart, who is accused of killing her, reported the 51-year-old missing three months earlier.

Near her body lay the remains of her beloved miniature dachshund, Boris.

During the opening of Stewart’s trial, St Alban’s Crown Court heard that the 56-year-old from Royston is accused of killing his future wife after he ‘secretly administered’ a sleeping drug in increasing amounts over time.

Ian Stewart is charged with murder (Picture: Masons)

Prosecutor Stuart Trimmer QC said: ‘The crown say this was simply a long-planned, deliberate killing, a cynically executed murder that had money as its driving motive.’

Jurors heard that the killing allegedly took place on April 11 at the home the couple shared, before Ms Bailey’s body was hidden in a septic tank below the garage.

Her death put the defendant in line for ‘substantial financial advantage’, the court was told.

Stewart is charged with murder, three counts of perverting the course of justice, preventing a lawful burial and fraud.

He denies all the accusations.

On the day the author was allegedly killed, her bank account was accessed, with a standing order to the defendant bolstered from £600 to £4,000, the court heard.

Helen Bailey was found in the septic tank of the couple’s home three months after she went missing (Picture: Masons)

Mr Trimmer said: ‘(The couple) had made financial arrangements that meant, in the event of the death of Helen Bailey before the wedding, Ian Stewart would obtain the house and a very substantial financial advantage.’

At the time of her killing, Ms Bailey was said to be worth more than £4 million.

The victim was said to have been concerned in the weeks leading up to her death that she was feeling unnaturally sleepy.

Mr Trimmer added: ‘All the typical activity that Helen Bailey engaged in ceased at about 11am April 11 2016.

‘The crown case is that, by early afternoon, the only other person in that house, Ian Stewart, killed her, probably by suffocation whilst she was sedated by the drugs he had administered for some time.’